This is relatively common with experimental therapies in trials, and thus shouldn't be interpreted as the final say on its usage.

Part of the reason why is that it's difficult to convince patients or providers to reach for the experimental treatment in trial before the current standard of care. Many first-line treatments began as second/third-line or salvage treatments before experiencing line promotion or (if surgery is involved) neoadjuvant promotion. Keytruda is a good example of this progression in action.